Electric furnace.



J. BLATCHFORD.

ELECTRIC FURNACE.

APPLICATION FILED AUG. 19, 1914.

fatented Mar. 2, 1915.

2 SHEETS-SHEET 2.

Fly. 5

25-U 26 ZJ\ wit eooes UNITED STATES PATENT onrron."

JOHN BLATCHFORD, OF OAK PARK, ILLINOIS.

ELECTRIC FURNACE.

Specification of Letters Patent.

Patented Mar. .2, 1915.

Application filed August 19, 1914. Serial No. 857,468.

The main objects of this invention are to provide an improved and simplified form of furnace of the above character especially adapted for laboratory use as well as commercial purposes, and having few and easily accessible parts adapted for ready control of temperature; to provide a furnace which may be usedadvantageously for ignitions and fusions, and for heat treatment in annealing and tempering tools and the like;

.to provide a casing of improved and durable construction and embodying improved means for distributing and retaining the heat in the furnace; and to provide an improved and more efficient arrangement and construction of heater element parts ada t ed to utilize within the furnace substantia ly all of the power taken from the source of current, and means for controlling the electrical relation of said parts to one another and to the source of power.

An illustrative embodiment of this invention is shown in the accompanying drawings, in which:

- Figure 1 is a side view of the furnace, the

left end being in elevation and the fight end in longitudinal vertical section on the line AA of Fig. 2. of the front or door end of the furnace. Fig. 3 is a fragmentary sectional view ofthe upper front part of the device on the line AA of Fig. 2. Fig. ,4 is like the left end of Fig. 1, but with thedoor open. Fig. 5

is a diagram showing the preferred arrangement of swltches, heater resistance mem bers and electrical. connections therefor.

' Fig. 6 is a perspective view of the stop catch Fig. 2 is an elevation view for the door counterbalance arm. Fig. 7 is a perspective view of the closure plug for the rear end of the oven. Fig. 8 is a perspective view of one of the pair of pivot bearing angles for the door. Fig. 9 is a simplified diagram of electrical connections.

In the construction shown, the furnace 1 is of the mufiie type and comprises a fireproof frame or casing 2 preferably rectangular and oblong in shape and-having openings 3 and 4 at its opposite ends, a door 5 being provided for the front opening 3 and a plug 6 for, the rear opening l.

The longitudinal walls of the casing 2 on all four sides are substantially double in character and each comprises an outer wall member, preferably of thin sheet metal, and a heavy inner wall of hard refractory material spaced therefrom, the outer covering preferably being formed integrally as a continuous outer shell or armor 7 from a single sheet of metal with its overlapping edges fastened together, as shown at S on the underside of the furnace. The inner wall member 9 is tubular and integral in character and is adapted to serve as a core or support for the heater resistance elements preferably wound thereon, as will be described.

The transverse members or ends 10 and 12 of the casing are preferably solid throughout and are formed to project somewhat at their edges 13 beyond the longitudinal walls to serve as hearing flanges or supports for the front and rear ends respectively of the furnace, and to protect the same. The said ends are each secured to the side walls by means of peripherally disposed angle bars 15 and by suitable fastening means 17 therefor, as rivets or screws. One flange of each angle bar lies against the back of the adj acent end wall flange 13 and the other angle flange lies against the plate 7 and preferably underlies the same.

vided for controlling and adjusting the cirand third resistances 22 and 23 being side a peripheral horizontally projecting rib adapted and arranged for seating the adjacent angle bars 15 on its outer side, together with the adjacent ends of the outer wall member 7, and for seating the inner wall member or core 9 on its inner side. The rib 20 on the front end is substantially similar to rib 20 on the rear end.

The heat generating resistance elements 21, 22 and 23 are each distributed spirally upon the core 9, the successive turns of the three unit spirals being arranged in turn or alternately so that the heat generated by each coil will be uniformly distributed throughout the whole length of the core, and so that the whole length of the furnace will be uniformly heated, regardless as to how many or which coilsare used, or vin what combination they are used.

Three single-pole double-throw knife switches 25, 26 and 27 are preferably procuit relation of the several resistance units with respect to each other, and to the source ofcurrent 28. Said switches are advantageously mounted on a separate base or block 30 of suitable insulation adapted to serve as a'support for the switch and-being adapted for mounting upon the side of the furnace, a plate 34 of insulation being interposed bejilzi ween wall shell 7 and blocks 30, as shown in 1g. 1. v

The electrical connections are as follows: The first resistance 21 is connected between one side 35 of the source of current and the middle post of the first switch 25, the second connected at one end of each to the middle post of the second switch 26, the opposite ends being connected respectively one to the middle post of the third switch 27, and the other to the opposite side 36 of said source, the first switch 25 having one outer post 25 connected to said opposite side 36 of the current" source and its opposite post 25" to the outer posts 26 and 27 of said second and third switches, the opposite outer posts 26 and 27 of said second and third switches being connected to the said one and opposite sides 35 and 36 of said source respectively. By means of this arrangement of connections between the three heater elements and switches, six different adjustments or steps may be had, resulting in six corresponding degrees of heat in the furnace.

The following table shows the relative 7 values of current and corresponding temperature for the six different steps attainable, it being understood that E represents the voltage of the current source, R the resistance ofcoil21, R the resistance of coil 22 and R" the resistance of coil 23, and that the respective currents for the several steps are indicated by I, I, and I I", I, and 1 The resistances of coils 21, 22 and 23 are preferably alike in value.

. Switch points Step. 01 OsecL Current.

E 1 z5 l d27 I=WF E 2 5and26 I= 8 25" 26 and 27" y I imes R plus B plus R" E E 4. '26 or 26". I or w,

u u I/ i E E E E 5 52125 or 26 I plus w or plus R7,

E E E 6 26" and 27" and 25'. 1 plus w p s I? The door 5 is formed and arranged to swing downward in opening from its normal vertical position of closure, and when open lies with its upper face in alinement with the furnace floor 38, as shown in Fig. 4, whereby it serves as. a shelf or hearth.

Pivot bearings of'an improved form are provided for mounting the door. Said bearings are disposed in horizontal alinement adjacent to the lower edge of the door on each side and are adapted to facilitate removing the door by lifting the same 05 from its bearings whenever desired. Each bearing comprises a stationary angle bar 41 disposed vertically and set in the side of the doorway with one flange facing forward and the other inward transversely of the opening. Each of said angle bars is provided with an inclined groove or slot 42 extending backward and downward in the inner flange. A pivot 45 projects horizon-. tally from each side of the door in registry with said slots and each pivot is adapted to coact therewith, said pivots resting in the bottom of said slots when the door is in place, but being slidable upward and forward therein for removal of the door.

Combined stop and counterbalance means are provided, comprising an arm 50 and stop 51, said arm having one portion 50 disposed horizontally across the front of the door to which it is rigidly secured, and having a projecting portion bent backward and having a weight 53 secured adjustably thereon adjacent to its outer or free end. Said arm on one side of the frame adjacent to the swinging portion of said arm, and in the path thereof, whereby movement of the door and arm is arrested when the" door comes to its horizontal position in opening. Said stop comprises a vertical flange 54 adapted for securing directly to the wall of the furnace and a horizontal arm 55, the outer end of which 55 is carried backward and downward to receive the door arm.- When the door is opened, the arm 50 comes to rest against the arm 55 back of the tip 55', and the weight 53 bears against said inclined tip.

The plug 6 at the opposite or rear end of the furnacecomprises a refractory core or projection 56, adapted to within the rear opening of the furnace in combination with a flat flange member or plate 57, to which it is rigidly secured, in any manner desired, as

by screws 59, the inner ends of which may be protected by fire clay, as shown' in Fig. 7. A handle 6(Hs provided on the outer side of the flange plate whereby the plug may be controlled.

Vent means are provided for the furnace, comprising a slot 63 formed in the core of the plug, which slot is preferably disposed in the upper side of'the core and the bottom of which-is inclined downwardly and inwardly, whereby the size of the vent may be adjusted by pushing the plug farther in or partially removing it to decrease and increase the size of the vent respectively, as will be apparent from Figs. 1 and 7.

The outer wall or shell 7 of the furnace is preferably made of sheet iron in order to secure great strength and stability. The core 9 for the resistance conductors is preferably made of alundum'in'order towithstand the intense heat when the furnace is running'at its maximum temperature. The resistance conductors are preferably laid in refractory cement 65 to maintain their spacing and to insure insulation from one another and from other parts of the furnace. The ends of the furnace may be formed of any hard and re fractory material but are preferably" formed of mineral board, so called. For the present purpose it has been found advantageous to use an asbestos compound known to the trade as transite asbestos wood. The same kind of material is also used preferably for the door and flange plate of the plug, as it is a good non-conductor of heat.

Mineral wool 67 is preferably used for packing in the space between the resistancewound core 9' and outer shell 7, although any heat resistent material having low conductivity for heat may be used. A refractory material ofhigh electrical resistance and capable of withstanding a high degree of temperature 'without oxidation is used for heater elements, a resistance conductor known to the trade as nichrome, being preferred.

This furnace is especially adapted for laboratory work and may be used to advantage for commercial purposes, both for ignitions and fusions and for annealing and tempering operations, particularly in the under all conditions and is substantially free from fire risk.

Although but one specific embodiment of this invention has been herein shown and described, it will be understood that numerous details of the construction shown may be altered or omitted without departing from the spirit of this invention as defined by the following claims I claim:

1. In a device of the class described, a-

source of current and three heater resistances adapted for connection to said source either independently or in connection with one another, in combination with three single-poledouble-throw switches, the first resistance being connected between one side of said source and the middle post of the first switch, the second and third resistances being connected at one end of each to the middle post of the second switch, the opbosite ends being connected, one to themiddle post of the third switch, and the other to the oppositeside of said source, the first switch having one outer post connected to said-op- 'posite side of the current source and its opposite post to an outer post, on each of said second and third switches, the opposite outer posts of said second and third switches being connected to the'said one and opposite sides of said source respectively.

'2. An electric furnace comprising an outer casing member of rectangular box shape having flanged closure ends which project laterally and serve as hearings to support the device, said ends each having an opening one of which is fitted with a swinging door and the other with a plug adapted and arranged for opening to a greater or lessdegree, in combination with arefractorfiv hollow core in said casing adapted and; ar-

ranged to serve as .an innerwall therefor,

and a plurality of heater elementseach distributed thereon and switching means there:

for, said furnace having a vent passage at its rear end adapted and arranged for adlar double-walled body portion, the outer and inner walls of which are spaced apart in combination with transversely disposed end members, each provided with a backwardly projecting rib adapted and arranged to re ceive the said wall members on their outer and inner edges respectively and to hold the same in definite spaced relation, heater resistance conductors disposed upon the outer surface of said inner. wall, said conductors -I being embedded in cement, refractory packcore of refractory material, in combination with three sections of heater resistance material carried by said core and each distributed uniformly thereon, a source of current, three single-pole double-throw knife switches mounted on said furnace, and electric circuit means connecting said resistances, switches and current source, whereby said resistances may be connected in various Ways with relation to each other and to the said" source to produce difierent temperatures.

Signed at Chicago this 12th day of Aug.

1914. JOHN BLATCHFORD. Witnesses 'FRED M. DAVIS, WILLIAM E. HANN., 

